Atoms, Molecules, Extended Structures and Stoichiometry

1. (Isotopes) Consider the
Br2 molecule. If there are two common isotopes, 79Br
and 81Br, how many physically distinguishable combinations of
Br atoms are there in Br2?

2, 3, 4

2. (Isotopes, natural abundance,
probabilities, mass spectrometry) If the two Br isotopes, 79Br
and 81Br, each has a natural abundance of about 50%, what is
the most likely molecular weight of Br2 molecules?

158 amu, 160 amu, 162 amu, all three are equally likely

Demonstration: Students in class flip coins twice in succession and
the numbers of two heads, two tails, and one head/one tail flips can be
tabulated by show of hands to make a connection with probabilities of independent
events being multiplicative.

7. (Unit cells; Ch. 3 "Companion")
A corner atom is part of how many unit cells? At-Seat Demonstration:
cubes like dice can be handed out for students to examine for this question.

1, 2, 4, 8

8. (Coordination number; Ch.
5 "Companion") In the two-dimensional square packing shown, what
is the coordination number of the central atom?

2, 4, 6

9. (Coordination number; Ch.
5 "Companion") At-Seat Demonstration: Give students 10
pennies (students can share a set of ten) and ask them to pack them at their
desks to determine the largest coordination number in two dimensions.

4, 6, 8, 9

10. (Unit cells, layer sequences;
Ch. 3 "Companion") In the figures below, how many atoms per unit
cell are present?

11. (Stoichiometry, empirical
formula, elemental analysis, atomic weights, magnetism) Demonstration
10.1 "Companion": On an overhead, show that with a magnet,
nickel powder is separable from the aluminum powder. Show that the pressed
bar comprising Ni and Al powder is also magnetic using the overhead projector.

The reaction goes from face-centered cubic Ni and Al to produce an alloy
of Ni and Al with the following layer sequence:

What is the empirical formula of the product?

NiAl, NiAl2, Ni2Al, Ni8Al

Run the reaction and show that the product bar is less magnetic using
the overhead projector.
Will the elemental analysis be the same for the bar before and after the
reaction?

Same, Different

Al atoms weigh about one-half of Ni atoms:

For a complete reaction (Ni + Al ---> NiAl), roughly what mass ratio
of reagents should be used?

equal masses of Ni and Alhalf the mass of Al as of Ni
twice the mass of Al as Ni

(An analogous set of questions could be developed for the quantitative reaction
of Fe and S.)

12. (Atoms, ions) How many
atoms are in the formula Al2(SO4)3?

3, 5, 17

How many moles of ions are there per mole of Al2(SO4)3?

2, 3, 5

20. (Ionization energy) A(g)
+ energy---> e- + A?(g). What is the charge, if any, on the product A?

+1, 0, -1

39. (Specific heat, heat capacity;
Ch. 2 "Companion") Setup: In solids, heat capacity near room temperature
often reflects the number of atoms in the solid. Demonstration 2.1
"Companion": Heat equal masses of Al and Pb in boiling water.
Transfer the Al to a beaker of room temperature water. Measure the temperature
increase with a digital thermometer. Before repeating with Pb transferred
to a separate beaker of the same volume of room temperature water, ask whether
the temperature change

will be greater with Pb, less with Pb, the same with Pb

42. (Elemental analysis, diffraction,
solid solutions; Ch. 3 & 4 "Companion") Sample A is an equimolar
physical mixture of Si and Ge. Sample B is a Si0.5Ge0.5
solid solution. Which measurements will be identical and which different
for the two samples?

43. (Vapor pressure) Demonstration: Drops of water and
ethanol are placed on an overhead projector and the ethanol drop is seen
to evaporate more rapidly. The graph below compares the vapor pressures
of ethanol and water. Which curve corresponds to ethanol?

A, B

Demonstration: Syringes are used to bring drops of H2O
and ethanol to the top of columns of Hg, as shown below. What will happen
to the heights of the Hg columns?

both column heights will be the same
the column below H2O is shorterthe column below EtOH is shorter

50. (Layer sequences; Ch.
3 & 5 "Companion") How many atoms are in the following layer
sequence of the diamond structure?

4, 6, 8, 13

What is the coordination number?

4, 6, 8

What is the coordination geometry?

tetrahedral, square, octahedral, cubic

53. (Layer sequences; Ch.
3 & 5 "Companion") What is the empirical formula of the solid
represented by the following layer sequence?